In recent years, a high dynamic range (HDR) image has attracted attention and is in practical use. The HDR image has a high dynamic range by being generated by synthesizing images of a plurality of frames having different exposure times and the like.
There exists an HDR compression device which performs HDR compression processing on the HDR image. The HDR compression device is used for displaying the HDR image on a device (for example, a display device) having a low dynamic range and the like. In the HDR compression device, for example, 24-bit image data is compressed into 8-bit image data. In the HDR compression device, data compression is performed by reducing a dynamic range using information on a luminance value of a frame image.
In a case where the frame image has color data, for example, RGB data, when extreme deviation in RGB colors is not present in the frame image, a ratio between pixel values between RGB data is maintained and image data is compressed by converting a luminance value Y of each pixel into a luminance value Y1.
However, when extreme deviation in the RGB colors is present in an original frame image, there is a problem that when the pixel value of each color of RGB of each pixel is recalculated based on the luminance value Y1 after conversion, the ratio between the pixel values between the RGB data is not maintained and a luminance value after compression is significantly decreased.
For example, in a case where only the luminance value (for example, 24-bit data) of one specific color is large in the original image and the pixel values of other colors are low, when the pixel value of each color corresponding to the luminance value Y1 after data compression is recalculated, only the color data of one specific color becomes large and overflow occurs in an internal register because the pixel values of the other colors are low, and as a result, the luminance value of the pixel is decreased significantly, so that the pixel may become like a black dot in some cases.